You don't have to pass a test to start bouldering, but for belaying, i.e. to make sure that if your climbing partner lets go of the wall they don't fall. There's a strong rope which your partner who's climbing on the wall is tied to with a knot. The belaying person holds hold the rope. But since it would be nearly impossible to just hold somebody directly without any means if they fall, the rope passes several loops of a carabiner-like device. That one and a ground rope (which attaches you to the ground) are attached to your harness that has a belt above your hips an two leg loops.
I had to learn a couple of knots and the right "language" how to communicate while your partner's climbing. For example, before your partner starts climbing, they ask "On belay?" and as the belaying person you answer "Belay on!" when you're ready and so on.
You don't have to have a partner necessarily, because there are auto-belays which belay you in the same way.
An climbing is great!! You have to use your entire body, concentrate and think about the next movement you make. Safety is super important - if one knot is not tight or wrong you might fall 6 m in our hall...